Filament yarns are conventionally packaged by being wound helically to form a bobbin of yarn on an axially-rotating cylindrical package support. Generally, for economical use of space, more than one package of yarn is wound simultaneously, using common or related drive and/or winding means. For simplicity, the present invention will be described specifically in relation only to previous winders that are designed for winding two yarn packages on supports that are located with their cylindrical axes located in parallel, usually at different heights. The helical winding configuration is obtained by a traverse guide that functions to sweep or to traverse the yarns from end to end of the parallel pair of yarn packages, and the traverse mechanism may guide the yarns directly to the packages or may guide the yarns first to a drive roll, or print roll, and thence to the packages.
Most present commercial winders (yarn winding apparatus) use a separate single-slotted traverse guide to wind each bobbin (i.e. package of yarn). The traverse guides have only one yarn (sometimes termed a threadline) in each guide-slot. A single traverse mechanism may supply more than one package from more than one traverse guide, each guide being appropriately located opposite its package. Thus (in most present commercially-available winders) there is only one yarn in each guide-slot, and so such winders are termed single end winders.
There have been some prior art winders that have been designed to wind two ends of yarn, with both ends of yarn advancing through the same single slot in the traverse guide to the rotating package. However, when two threadlines occupy a common guide slot, it is found that threadline interactions cause package defects known as overthrown ends, in which a short length of yarn in a reversal "falls" off the end of the package and lies along a chord across the end of the package. Such defects are more frequent with double end winding, than with single end winding. A further defect, that occurs when unwinding yarn packages, especially at very high speeds, such as 1,000 mpm, is known as shelling, when more than one loop of yarn comes off the package at the same time, and the extra loops tend to snag, e.g. on guides, get tangled, or cause sudden tension drops that can result in difficulties downstream. Increasing the helix angle can reduce such defects, but leads to other problems, that are well known. A further drawback is a package defect known as a doubleend pickup in which the yarn lines intertangle, breaking one yarn line, which then causes both yarn lines to wind to a single package instead of separating with one yarn line per package.
Accordingly, because of such defects, dual-slotted devices have previously been proposed wherein the slots are located close together, as suggested, for example, in IWKA French Certificate of Utility 2,146,200 and Lyons, U.S. Pat. No. 4,187,994. The IWKA French Certificate shows guide-slots on two different levels, i.e. an outer guide-slot (referenced 6a) and a lower guide-slot (referenced 6b), located to one side of the upper guide-slot, and the threadlines are kept separate before approaching the slots by stationary means, preferably a vertical plate (referenced 7), located upstream. Lyons shows an outer guide-slot at the outer end of a traverse guide-plate, which is of generally isosceles triangular shape, while another guide-slot is located in the sloping side of the guide-plate, i.e. to one side of and somewhat below the outer guide-slot, and an elongated guide member is provided whereby only the outer slot is exposed, so that a first yarn can only be strung up in this outer slot, and then the other lower slot (in the sloping side of the guide plate) is also exposed, so the second yarn may be strung up in this second slot.
Previous suggestions for dual-slotted traverse guides have not proved entirely satisfactory, e.g. in complications, flexibility, maintenance problems and curing the defects referred to (for a common guide-slot); so it is an object of the present invention to provide a better system for winding with a dual-slotted traverse guide. For convenience, however, reference may be made to Lyons, the disclosure of which is hereby incorporated by reference.